This website provides a simple API to lookup an Amazon Standard Identification Number (ASIN) from a UPC.
Use this form to convert a UPC to an ASIN:
You can submit a simple GET query to the REST to return an ASIN like this:
The body of the resulting page will contain the ASIN corresponding to the UPC specified.
You can see the source for this project on GitHub.
You can file bugs or request new features using Issues.